This invention relates to a package for a fiber optic semiconductor device and, in particular, to a package having improved thermal characteristics.
A continuing concern in the manufacture of semiconductor packages for fiber optics is the amount of light launched into the system fiber. If greater luminous flux were available, one could use longer lengths of system fiber. There are two ways to increase the luminous flux in a fiber. One is to increase the luminosity of the source. The other is to improve the coupling between the photoactive area of the semiconductor and the optical fiber. This invention relates to the former and is useful for both light emitting and light sensing semiconductor devices.
In a typical application, fiber optic semiconductor devices are mounted parallel to printed circuit boards, e.g. in a fiber optical data link. In such applications, it is desirable to retain the compactness of the present ferruled semiconductor device as well as the capability for horizontal mounting, particularly since many systems have closely spaced printed circuit boards with expensive board area.
With fiber optic sources, i.e. light emitting devices, a problem develops in that the amount of light produced depends on the input power or, more specifically, on the forward current through the diode. It is desired to operate at the highest forward current possible, without compromising reliability. The maximum forward current is limited by the rise in junction temperature, which is proportional to the power dissipated by the junction times the thermal impedance of the package. The thermal impedance of a package is dependent, in part, on the size of the package and, in part, on the package materials and design. Thus the problem is to dissipate larger amounts of power in packages of a given size and shape, while maintaining low cost. While mounting a device to a heatsink instead of directly to the printed circuit board would aid heat dissipation, the advantages of compactness and low cost of the device would be lost. Alternatively, as others have done in the art, one can simply make the package bigger. Making the package bigger would require a plurality of different sized connector hardware, all of which must be maintained in inventory, which is undesirable. Also making the package bigger increases cost and board usage.
In view of the foregoing, it is an object of the present invention to provide a low-cost package having low thermal impedance.
Another object of the present invention is to provide a package having reduced thermal impedance and the same outside dimensions as previous packages.
A further object of the present invention is to provide a more luminous fiber optic semiconductor device.
Another object of the present invention is to provide a more luminous fiber optic semiconductor device adapted to use the connector as a heatsink.
A further object of the present invention is to provide a plastic package of reduced thermal impedance, acting as a heat spreader for the semiconductor element within.